that clearly illustrate how to specify fan performance. Another important decision that must be made by the fan specifier is the method of control to be used for the fan. Common means of control are listed below, some of which can be combined: ■ Outlet damper/system damper ■ Inlet box dampers ■ Variable inlet vanes ■ Variable speed or multiple speeds ■ Blade angle change. Figure 2 illustrates common fan accessories used for fan control in industrial process and power generation applications. Figure 3: Model test of a rotor retrofit, where a fan wheel made by one manufacturer was installed in an existing fan casing made by a different fan manufacturer. In such cases, it is common for the customer to specify that a model test be done because the fan laws do not apply to such situations. Image courtesy of FlaktWoods. on the expected system curve, so the fan designer can select a fan that is appropriate for all of these conditions. AMCA Publication 801 discusses these concepts and provides data sheets Once provided with all of the required system performance parameters, the fan designer can proceed to select a fan that is appropriate. This is normally done using the laws of geometric similitude, commonly referred to as the “Fan Laws,” as outlined in AMCA 802. These laws allow prediction of the performance of actual fans from model fan data. The testing of model fans is the state-ofthe-art approach for determining fan performance. This testing can be conducted in accordance with AMCA Standard 210 or www.info.hotims.com/44636-12 10 Fa l l 2 0 1 3 a m c a I n t e r nat I o na l inmotion w w w. a m c a . o r ghttp://www.tcf.com http://www.tcf.com http://www.info.hotims.com/44636-12 http://WWW.AMCA.ORG